Since {HEAD ~ the achievement} of coherency is distributed in {TAIL ~ time} and space, the node controller helps to maintain cache coherency 
Since { HEAD ~ the achievement } of coherency is distributed in { TAIL ~ time } and space , the node controller helps to maintain cache coherency
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH