Black Mastic? Haven't seen that one. But normerally it takes a hammer, chisel and a hand held 4" flooring scraper to remove the adhesive to get a clean subfloor on concrete.

I'm new here and don't know how to navigate this site so if I missed anything...sorry. Many forums allow you to go back and FWD. This is kinda a test

Had the same thing in my house. No simple solution. I used a floor scaper that had replaceable blades. Mastic is usually put on with a notched trowel, and if you scrape with the grain of the notches it usually comes right up. Anything that sticks after that is probably as sound as the concrete underneath.