I don't think I've seen an entire family scratched out, but I've seen what seems to be census-takers trying to remove a single person. For example: in the 1850 census of Campbell co. GA, my 4x-great-grandparents appear with their blended family, including a scratched out daughter named Martha (the scratching didn't work very well). I have wondered what happened. Did the census-taker accidentally record a neighbor girl as one of their children, and upon being told of the mistake, tried to correct it? Did they have a daughter named Martha who had died very recently and the census-taker wasn't sure whether to count her?