We've black and white checkerboard style vinyl flooring in our kitchen. It gets a good mop with Flash at least weekly and I get down on hands and knees and scrub the edges and anywhere else I need to, but the few white squares directly in front of the sink have started to look permanently grubby despite these efforts and no amount of scrubbing (with cloth, mop or scrubbing brush) makes any difference. It's a big area to floor and the rest of it is fine, so I'm reluctant to spend a fortune reflooring if there's some miracle cleaning product that could salvage it. Any suggestions? Or am I going to have to but the bullet and accept it's just beyond that now?