Diluted brick acid aplied from a watering can, then pressure wash again. The cement would have stained the blocks and the acid burns a very thin layer off the surface. test small area first to make sure you are happy the result and adjust dilution rates/dwell time.
After pressure washing a block pave drive you need to revisit after it has dried properly and brush in some kiln dried sand or geo-fix. The sand is an improtant part of the structure of the drive and you are leaving yourself open to having to pay for drive having to be relaid if you don't.