I'm interested in knowing this as well.
We are unable to use multicast here because we have several developers on the same subnet running many versions of jboss. But when I use the TCP configuration jboss clustering itself works fine but jboss cache just seems to not work (as a cluster) at all. The updates to one host just don't get replicated to the other (I am using REPL_SYNC, and I get no exceptions). Funny thing is I see them find each other in the server log!
Maybe I am just misunderstanding portions of the config file and the provided documentation.
The following properties must be set in treecache.xml for cache replication to take place -
1. CacheMode= REPL_SYNC
2. ClusterName - All the nodes which are to form a cluster must have the same name
3. A proper cluster config