Back in the Early 2000's I bought a built in 1994 house in Florida that was all glued down sheet vinyl on concrete. I wanted to tile it and ripped up this ugly black and white vinyl. But the glue would not come off easily. Now mind you it was over 2000 square feet. Scraping it did nothing and I was at my wit's end. So someone had recommended a grinder also but just before we were heading to rent one I had a 5 gallon bucket full of water that I accidentally knocked over and got a good portion of the glue wet. After a little bit of time my friend took a scraper and low and behold the glue just came up.

Once we figured out it was water based glue we were able to remove the glue with no fuss at all with a big scraper. Saving a big mess with a grinder. You may want to see if the glue is water based by putting some water on it and wait a bit. I still live in the house and the tile is holding up great. Oh, btw why do you want to put ditra on a concrete floor? I don't see a need in that unless maybe your heating it.