Sorry, I'm a little bit wrong about your caching. I have just figured out that because each zimbra-store handles a different set of accounts so what are stored in LRU are totally different, regardless of LDAP or MySQL data.
So the best caching stragedy is to use LRU for server-specific information such as those in dc=domain,dc=com (I mean user's accounts) and use memcached for global information such as those in cn=zimbra (domains, servers, cos...). IMHO, it doesnt worth to integrate memcached for just cn=zimbra data. It seems that the whole idea of using memcached together with Zimbra is broken
.
Sorry for wasting your time reading my meaningless words.
-g