Stripping off rough sheets, he did push-ups until his arms shook, then stood in the dark and tried to forget the feel of blackness and quiet and memories scratched through to white.
What does the highlighted part mean?
That highlighted line is not a common expression. I would venture to say it is a unique creation of the author, like poetry.
What ¨memories scratched through to white¨ evokes for me is the idea that they are memories he has tried very hard to erase (painful, disturbing memories.)