I would try various solvents, start with mild and work your way up. Even things like automotive brake or carburetor cleaner have worked for me. As someone else said, use cotton swaps and hopefully something will dissolve whatever it is, scrubbing is not a good idea. It's also a good idea if you start using harsher solvents to remove the lens element. When it's clear nothing is going to dissolve the haze, I've used cerium oxide glass polish, knowing I was removing the front coating, to make a lens usable again. It's better than throwing it away and I don't think one surface being uncoated is the end of the world.