Re: Official BBC Tweet (SPOILERS)
^^Why would their memories need to be wiped? There's never been any indication that happens to any of the Doctors or companions in the multi-Doctor stories, except maybe the Second Doctor in The Two Doctors. In fact, it's exactly because the Fifth Doctor remembers that resolved the situation in Time Crash.
"Internet message boards aren't as funny today as they were ten years ago. I've stopped reading new posts." -The Simpsons 20th anniversary special.