How can you soften granulated sugar that has hardened?

Putting chunks of sugar in a food processor works, but it scratched the inside of my processor so I did it the old fashion way. I broke the block into Baseball sized chunks with and ice pick and put these inside an old tee shirt. I used the side of a hammer to brake these up. Holding the arms and tail of the tee shirt, I poured the contents through the neck hole into a large pan. There were still pea sized lumps so a held a colander over another pan and sifted out the lumps. (Holding a vibrator against the colander makes this go really fast.) Then I used the back side of an ice-cream scoop to brake up the remaining lumps in the colander.