public void purge()
    {
        final Lock lock = MUC_HISTORY_CACHE.getLock(roomJID);
        lock.lock();
        try {
            MUC_HISTORY_CACHE.put(roomJID, CacheableOptional.of(null));
        } finally {
            lock.unlock();
        }
    }
Removes all history that is maintained for this instance.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/HistoryStrategy.java