Not necessarily - infants brains are to plastic to retain memory, so it's entirely possible it just erased itself all on it's own.

Uhm. I've been entertaining the idea that Slytherin did something to his descendants to make them immune to memory magics. In which case, maybe the entire point of horcruxing an infant was to get a fork of his mindstate without his memories, because the direct approach would not cut it.

On the other hand, this chain of inferences is getting a wee bit longer than I am at all comfortable with.