Correctness of Linearizability vs Sequential consistency in replication
A Sequential Consistent (SC) system should behave as if there is just a single copy of the data.
So lets try to determine a possible memory order for your scenario:
1:client2:read(y=0)
2:client2:read(x=0)
3:client1:write(x=1)
4:client1:write(y=2)

This is valid according to SC. Keep in mind that the real time order of requests, doesn't need to preserved. So perhaps the client2.read(x=1) happened later than the client1.write(x=1), it can be ordered in the memory order before the write.
Lets change the example a bit to make it more interesting:
1:client1:write(x=1)
2:client1:write(y=2)
3:client2:read(y=2)
4:client2:read(x=0)

This example isn't SC because the read of x=0, doesn't see the most recent write before it in the memory order. It should have seen x=1. And this is the consequence of the lack of coherence (so what you could get with replicas being out of sync).