Each processor has {HEAD ~ its own cache directory} and image directory that duplicate {TAIL ~ each other non} atomically 
Each processor has { HEAD ~ its own cache directory } and image directory that duplicate { TAIL ~ each other non } atomically
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH