I recently removed vinyl flooring that was installed when my house was built in 1955. What I found was some scarey black tar paper on top of adhesive. My husband and I tried scraping for a whole day with no luck. What I finally did was score the area the best I could and then poured white vinegar on it and let it sit over night. It worked! The vinegar ate the adhesive so the paper then peeled right up. I originally thought that I'd have to replace the subfloor for sure. But honestly soaking the area with plain old white vinegar really worked. Good luck!