Reading another great post of Ivan Pepelnjak from blog.ioshints.info, I followed a link to Cisco website with an article about Unicast Flooding in Switched Campus networks. When I looked at "Cause 1: Asymmetric Routing" diagram, I came to conclusion, that the packets won't be flooded, as it said there in article, because at the reverse route, S1 will reply with its own mac-address to RouterB ARP-request, so switchB will have it in its CAM table, so it will forward the packet to the proper interface toward SwitchA.
What do you think? Am I wrong?
Link, again.
P.S. I even lab'ed it. No unknown unicast happened.
UPD.: I came to yet another conclusion: the situation described above can be true, if entry in the switch's CAM table is timed-out. If the router still has the mac-address of S1, then it will send the packets without subsequent arp-requests, however the switch will now flood the unicast frames.
