DOCS-14619 clarify dropDatabases sharded cluster procedure

Author: andf-mongodb

source/includes/warning-dropDatabase-shardedCluster.rst

@@ -1,10 +1,55 @@
-.. warning::
-
-   If you drop a database and create a new database with the same name, you
-   must either restart all :binary:`~bin.mongos` instances, or use the
-   :dbcommand:`flushRouterConfig` command on all :binary:`~bin.mongos`
-   instances before reading or writing to that database. This action
-   ensures that the :binary:`~bin.mongos` instances refresh their
-   metadata cache, including the location of the :ref:`primary shard
-   <primary-shard>` for the new database. Otherwise, the
-   :binary:`~bin.mongos` may miss data on reads and may write data to a wrong shard.
+If you intend to create a new database with the same name as the dropped
+database, you must follow these additional steps for using the
+:dbcommand:`dropDatabase` command with MongoDB 4.0 or previous:
+
+#. Run the :dbcommand:`dropDatabase` command on a
+   :binary:`~bin.mongos`.
+
+#. Connect to each shard's :term:`primary` and verify that the
+   namespace has been dropped. If it has not, rerun the
+   :dbcommand:`dropDatabase` command again directly from the
+   :term:`primary`.
+
+#. Connect to a :binary:`~bin.mongos`, switch to the
+   :term:`config database`, and remove any reference to the removed
+   namespace from the ``databases``, ``collections``, ``chunks``,
+   ``tags``, and ``locks`` collections:
+
+   .. code-block:: javascript
+
+      use config
+      db.collections.remove( { _id: /^DATABASE\./ }, {writeConcern: {w: 'majority' }} )
+      db.databases.remove( { _id: "DATABASE" }, {writeConcern: {w: 'majority' }} )
+      db.chunks.remove( { ns: /^DATABASE\./ }, {writeConcern: {w: 'majority' }} )
+      db.tags.remove( { ns: /^DATABASE\./ }, {writeConcern: {w: 'majority' }} )
+      db.locks.remove( { _id: /^DATABASE\./ }, {writeConcern: {w: 'majority' }} )
+
+   Where ``DATABASE`` represents the namespace of the database you
+   just dropped.
+
+#. Connect to the :term:`primary` of each shard, and remove any
+   reference to the removed namespace from the ``cache.databases``,
+   ``cache.collections``,  and ``cache.chunks.DATABASE.COLLECTION``
+   collections:
+
+   .. code-block:: javascript
+
+      db.getSiblingDB("config").cache.databases.remove({_id:"DATABASE"}, {writeConcern: {w: 'majority' }});
+      db.getSiblingDB("config").cache.collections.remove({_id:/^DATABASE.*/}, {writeConcern: {w: 'majority' }});
+      db.getSiblingDB("config").getCollectionNames().forEach(function(y) {
+         if(y.indexOf("cache.chunks.DATABASE.") == 0)
+          db.getSiblingDB("config").getCollection(y).drop()
+       })
+
+   Where ``DATABASE`` represents the namespace of the database you
+   just dropped.
+
+#. Use the :dbcommand:`flushRouterConfig` command on **all**
+   :binary:`~bin.mongos` instances before reading or writing to that
+   database.
+
+These steps ensure that all cluster nodes refresh their metadata cache,
+which includes the location of the :ref:`primary shard<primary-shard>`
+for the new database. Otherwise, you may miss data on reads, and may not
+write data to the correct shard. To recover, you must manually
+intervene.

source/reference/command/dropDatabase.txt

@@ -77,7 +77,7 @@ User Management
 Replica Set and Sharded Clusters
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. versionchanged:: 3.6
+.. versionchanged:: 4.0
 
 Replica Sets
    At minimum, the method waits until all collection drops in