The reIndex method is on the collection.

Note: AFAICT, this change will break a URL, but will make the URL for
reIndex more consistent with the URLs for other collection methods.

Author: Richard Kreuter

source/reference/method/reIndex.txt

@@ -1,10 +1,10 @@
 =========
-reIndex()
+db.collection.reIndex()
 =========
 
 .. default-domain:: mongodb
 
-.. method:: reIndex()
+.. method:: db.collection.reIndex()
 
    This method drops all indexes and recreates them. This operation
    may be expensive for collections that have a large amount of data