To bind or unbind user tables, indexes, or text or image objects, the cache binding commands must have an exclusive table lock on the object. If a user holds locks on a table, and you issue sp_bindcache, sp_unbindcache, or sp_unbindcache_all on the object, the system procedure sleeps until it can acquire the locks it needs.
For databases, system tables, and indexes on system tables, the database must be in single-user mode, so there cannot be another user who holds a lock on the object.
