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