(PECL memcached >= 2.0.0)
Memcached::deleteMultiByKey — Delete multiple items from a specific server
   Memcached::deleteMultiByKey() is functionally equivalent to
   Memcached::deleteMulti(), except that the free-form
   server_key can be used to map the
   keys to a specific server.
  
server_keyLa chiave che identifica il server su cui salvare il valore. Invece di effettuare li'hashing sulla chiave dell'elemento, si effettua l'hashing della chiave del server al momento di decidere con quale server memcached comunicare. Questo permette di raggruppare gli elementi correlati ad un singolo server ottenendo maggiore efficienza nelle operazioni multiple.
keysThe keys to be deleted.
timeThe amount of time the server will wait to delete the items.
Nota: As of memcached 1.3.0 (released 2009) this feature is no longer supported. Passing a non-zero
timewill cause the deletion to fail. Memcached::getResultCode() will returnMEMCACHED_INVALID_ARGUMENTS.
   Returns an array indexed by keys. Each element
   is true if the corresponding key was deleted, or one of the
   Memcached::RES_* constants if the corresponding deletion
   failed.
   
   The Memcached::getResultCode() will return
   the result code for the last executed delete operation, that is, the delete
   operation for the last element of keys.
  
