I too ran into this in my bathroom. Ripped up the Lino and plywood underneath. Ran into a thick coating of a tar-like substance. As I was refinishing the floor, I used BIX Stripper (better to use the Heavy stuff ( $18 +/- 1 gal.). This worked OK. Lay it on thick let stand for about 20 minutes, scrape off, and repeat. You may have to do this 5+ times to completely remove the "tar". I did a 5' X 5' bath in about 3 hours. Took a while, but I don't know of any other method. This may or may not work, depending on the size of your kitchen, and the work you are willing to put into it. Mine was pine as well.