I have heard the phrase 'down the memory hole' used before, and I believe it to have originated in the novel 1984 by George Orwell, but I'm not 100% sure the definition I've found is right:
memory hole noun a piece of one's memory that seems to be missing; also, a place where lost memories seem to go
Word Origin modeled upon black hole
memory hole. Dictionary.com. Dictionary.com's 21st Century Lexicon. Dictionary.com, LLC. http://www.dictionary.com/browse/memory-hole (accessed: April 21, 2016).
My understanding was that the phrase refers to something deleted or removed because something about it was likely to cause embarrassment or lost reputation to a person, or to persons, related to it.
Like if there was a book, or a photograph, or even a post on here, which was completely erased, because some people didn't want to be associated with it in some way...
My feeling is this rendering could use some tuning, though, so I was wondering if anyone could provide a more authoritative definition.