2.4.2.3.1. Example: Effects Of Intel 80x86 Memory Ordering Model
A       dd      0
B       dd      0

Executed on one processor:

        mov     [A], 1
        mov     eax, [B]

Executed on another processor:

        mov     [B], 1
        mov     eax, [A]

It is possible for both processors to finish with EAX containing 0.