synchronized ( this.dcLock ) {
            CacheEntry<DfsReferralDataInternal> ce = this.dcCache.get(dom);
            if ( ce != null && System.currentTimeMillis() > ce.expiration ) {
                ce = null;
            }
            if ( ce != null ) {
                DfsReferralDataInternal ri = ce.map.get(DC_ENTRY);
                if ( ri == NEGATIVE_ENTRY ) {
                    return null;