JBoss Cache is designed to be a peer-to-peer library where every user of the cache is a member of the cluster. Not a client-server type architecture.
That said, it can very easily be made into a client server architecture. A server could run JBoss Cache and use a CacheWrapper to expose the cache as a server.
You could implement the CacheWrapper in RMI, an EJB, CORBA, a Web Service, etc etc. Depends on how you'd like your clients to connect to the cache.