private static boolean isClusterableCache(final Cache cache) {
        return cache instanceof CacheWrapper && !localOnly.contains(cache.getName());
    }
Indicates if the supplied Cache is "clusterable". This is used to determine if a cache should be migrated
between a {@link DefaultCache} and a clustered cache when the node joins/leaves the cluster.
<p>
A cache is considered 'clusterable' if;
<ul>
    <li>the cache is not a 'local' cache - which apply to the local node only so do not need to be clustered, and</li>
    <li>the cache is actually a {@link CacheWrapper} which wraps the underlying default or clustered cache</li>
</ul>

@param cache the cache to check
@return {@code true} if the cache can be converted to/from a clustered cache, otherwise {@code false}
xmppserver/src/main/java/org/jivesoftware/util/cache/CacheFactory.java