diff --git a/conf/default.conf.php b/conf/default.conf.php
index 4e88b69d10..078c4e128d 100644
--- a/conf/default.conf.php
+++ b/conf/default.conf.php
@@ -557,7 +557,8 @@ return array(
   // against each regexp in order until one matches. The default configuration
   // uses a width of 100 for Java and 80 for other languages. Note that 80 is
   // the greatest column width of all time. Changes here will not be immediately
-  // reflected in old revisions unless you purge the render cache.
+  // reflected in old revisions unless you purge the changeset render cache
+  // (with `./scripts/util/purge_cache.php --changesets`).
   'differential.wordwrap' => array(
     '/\.java$/' => 100,
     '/.*/'      => 80,
diff --git a/scripts/util/purge_cache.php b/scripts/util/purge_cache.php
new file mode 100755
index 0000000000..8db1063a54
--- /dev/null
+++ b/scripts/util/purge_cache.php
@@ -0,0 +1,135 @@
+#!/usr/bin/env php
+<?php
+
+/*
+ * Copyright 2011 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+$root = dirname(dirname(dirname(__FILE__)));
+require_once $root.'/scripts/__init_script__.php';
+
+phutil_require_module('phutil', 'console');
+phutil_require_module('phabricator', 'storage/queryfx');
+
+$purge_changesets   = false;
+$purge_differential = false;
+$purge_maniphest    = false;
+
+$args = array_slice($argv, 1);
+if (!$args) {
+  usage("Specify which caches you want to purge.");
+}
+
+foreach ($args as $arg) {
+  switch ($arg) {
+    case '--all':
+      $purge_changesets = true;
+      $purge_differential = true;
+      $purge_maniphest = true;
+      break;
+    case '--changesets':
+      $purge_changesets = true;
+      break;
+    case '--differential':
+      $purge_differential = true;
+      break;
+    case '--maniphest':
+      $purge_maniphest = true;
+      break;
+    case '--help':
+      return help();
+    default:
+      return usage("Unrecognized argument '{$arg}'.");
+  }
+}
+
+if ($purge_changesets) {
+  echo "Purging changeset cache...\n";
+  $table = new DifferentialChangeset();
+  queryfx(
+    $table->establishConnection('w'),
+    'TRUNCATE TABLE %T',
+    DifferentialChangeset::TABLE_CACHE);
+  echo "Done.\n";
+}
+
+if ($purge_differential) {
+  echo "Purging Differential comment cache...\n";
+  $table = new DifferentialComment();
+  queryfx(
+    $table->establishConnection('w'),
+    'UPDATE %T SET cache = NULL',
+    $table->getTableName());
+  echo "Done.\n";
+}
+
+if ($purge_maniphest) {
+  echo "Purging Maniphest comment cache...\n";
+  $table = new ManiphestTransaction();
+  queryfx(
+    $table->establishConnection('w'),
+    'UPDATE %T SET cache = NULL',
+    $table->getTableName());
+  echo "Done.\n";
+}
+
+echo "Ok, caches purged.\n";
+
+function usage($message) {
+  echo "Usage Error: {$message}";
+  echo "\n\n";
+  echo "Run 'purge_cache.php --help' for detailed help.\n";
+  exit(1);
+}
+
+function help() {
+  $help = <<<EOHELP
+**SUMMARY**
+
+    **purge_cache.php** [--maniphest] [--differential] [--changesets]
+    **purge_cache.php** --all
+    **purge_cache.php** --help
+
+    Purge various long-lived caches. Normally, Phabricator caches some data for
+    a long time or indefinitely, but certain configuration changes might
+    invalidate these caches. You can use this script to manually purge them.
+
+    For instance, if you change display widths in Differential or configure
+    syntax highlighting, you may want to purge the changeset cache (with
+    "--changesets") so your changes are reflected in older diffs.
+
+    If you change Remarkup rules, you may want to purge the Maniphest or
+    Differential comment caches ("--maniphest", "--differential") so older
+    comments pick up the new rules.
+
+    __--all__
+        Purge all long-lived caches.
+
+    __--changesets__
+        Purge Differential changeset render cache.
+
+    __--differential__
+        Purge Differential comment formatting cache.
+
+    __--maniphest__: show this help
+        Purge Maniphest comment formatting cache.
+
+    __--help__: show this help
+
+
+EOHELP;
+  echo phutil_console_format($help);
+  exit(1);
+}