This is the same as what the bus (or the L3 directory) does to maintain a sequential timeline: only a single processor can operate at the same time.
chamusyuan
We can see from this that the only thing guaranteed is the program order within processors but we do not know which processor gets picked and run first in this case.
pintos
Sequential consistency is what programmer's typically think of since all single-threaded code we run on Intel processors runs in a sequentially consistent manner.
This is the same as what the bus (or the L3 directory) does to maintain a sequential timeline: only a single processor can operate at the same time.