The advanced directory protocol described above relies on a point-to-point ordered interconnect to ensure correct operation. Assuming the initial cache contents of Figure 4.42 and the following sequences of operations, explain what problem could arise if the interconnect failed to maintain point-to-point ordering. Assume that the processors perform the requests at the same time, but they are processed by the directory in the order shown.
a. P1: read 110 P15: write 110 <-- 90
b. P1: read 110 P0: replace 110