Coherency != Memory Consistency
Assume A and B initially 0
P0
$ Mem
Directory
Controller
P2
$ Mem
Directory
Controller
Interconnection Network
P1
$ Mem
Directory
Controller
A=1; while (A==0)do;
B=1;
while (B==0)do;
print A;
A=1;
B=1;
A=1;
Delay
Print 0