In US English, scrap paper would be the pieces of paper that were not used or partially used on something, say a book or a cutout. And scratch paper is closer to the meaning that the previous answers refer to.
So, Mexico being closer to the US, we have adopted a similar meaning as they are using, and it may be adequate and even understandable almost anywhere.
So instead of "trabajo en sucio" we use borrador (draft)
For scrap papers we use retazos sobrantes retazos de papel or simply retazos (literally leftover pieces) and it applies to any flat or sheeted material such as plywood or fabric, too; as long as they are leftover pieces of a larger stock material, written on, or otherwise =)