When using OSCache as the cache provider for Hibernate, the caches are not kept in sync in a cluster. This is because if an object is modified on one node, no notification is sent to the other nodes to update their cache for that object. They therefore maintain the old object in their cache, which is out of sync with the database. This can be very dangerous for data.
In order to correct this, I have extended JavaGroupsListener:
1) Add anew Event type: REMOVE_KEY
2) Send out REMOVE_KEY when a cache is updated locally (not added). Currently it does nothing on update.
3) On receiving a REMOVE_KEY notice, it removes the keyed cache entry. This requires a modification of Cache in OSCache to make removeEntry public instead of protected.

Removal of the entry, rather than flushing, is necessary to keep the nodes from sending an update event to the cluster when they reload the flushed entry, which leads to endless propogation of the update and undermines the purpose of a cache. Removing the entry avoids this, as the nodes do an add, and not update, on the next load of the entry. Adds are not broadcast, as they are of only local interest.

I also modified the Hibernate3 OSCache and OSCacheProvider sources to implement regions, as stated on the wiki for Hibernate 2.1 I will submit those changes on their JIRA.