In one embodiment, each global interface includes a request agent , {HEAD ~ a directory agent} and {TAIL ~ a slave agent}  
In one embodiment , each global interface includes a request agent , { HEAD ~ a directory agent } and { TAIL ~ a slave agent }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH