I made some mistakes in the above post, and I apologize - I am new to JBossCache.
I programmatically set the cache mode to "local". Also, multicast won't work in our environment (the server instances reside on separate subnets.)
Use a TCP configuration for JGroups if you can't use mcast (see www.jgroups.org for docs on how to do this)
Set your cache mode to REPL_SYNC (better via the config than programmatically - gives you more flexibility)
You don't need to tweak your cache loader config for clustering unless both nodes write to the same file store.