"Acetone is the solvent used to thin/remove most spray foams, and can be effective even when they have dried. " Once polyiso foam (the common can stuff) has cured acetone will no longer dissolve it. It will dissolve the uncured foam. There is NO solvent for many of the foams once curing has completed. These are on-way chemical reactions. unless you want to go after strong acids and bases.

It looks like real marble to me. Try this first. Take mild dish soap (Ivory)dilute in a spray bottle. Wet the stone well and then do a light scrubbing with a nylon bristle brush. The yellowing likely will NOT be removed by regular cleaning as it will likely need the application of a "poultice" to "draw" the stain out of the pores of the stone crystals. If it lightens with light cleaning it may make you happy but other wise cleaning with a cleanser that can float the contamination up and out and this time WITHOUT detergents. If you would like the name or other methods on the poultice let me know Stan

I have a polished nickel kitchen faucet. It started to get marks that would not come off. When I asked the store where I purchased it they told me nickel is like silver - it is a "living" metal. It basically tarnishes like silver. They told me silver cleaner was not strong enough for nickel and I needed a metal cleaner. I purchased one at the local hardware store. My nickel looks amazing. I only have to deep clean it a few times a year. I found this green cleaner which does a very good job but not quite as good as the metal cleaner. Not sure where you can get it where you are. I actually polish my silver with this and many other jobs  itÂs a great cleaner. Use something mild on your marble. Many things will "etch" the finish of marble (vinegar for example). My husband did it to my new master bathroom counter right after we got it. Marks are still there today  sigh  Here is a link that might be useful: green cleaner

You need a stone restoration specialist clean and to repolish the entire floor with diamond polishing pads. That isn't DIY.