In Logic I just cut and paste, typically to a new sheet. I'm sure that can't be more than five times more difficult in DxD : )
Another option in Logic is to make a copy of the schematic, then delete everything not in your block. ASCII out your block and you can import it back in as needed. Now that I write this, I don't think DxD has an ASCII option though. Sorry.
The Reuse feature in Layout is very nice.
Good luck.