Harry Potter blood purity question?

Question

So I've been re-reading the HP novels as of late and the topic of blood purity intrigued me after I supplemented the novels with info on the matter. I first became interested in this after reading that Harry and Ginny's children are considered to be "half-blood." As far as I have gathered from the books and Rowling's statement on the matter, blood purity is usually traced back 2 generations to the grandparents. I would assume this is more or less the general wizarding consensus excluding various extremists like the Blacks, Malfoys, and Gaunts. I've read that no family's blood is completely pure by the time of the novel, even if they pretend it is and it's been revealed by several characters that fanatics will just ignore any muggle relations within their family. It seems an awful lot to me like the One Drop Rule... That even if you had a great-grandparent that was black, you in turn would technically be considered black as well. My question is, could a half-blood eventually "purify" their blood again by marrying a pure-blood and their descendants doing the same? For example, if Harry's daughter, Lily married Malfoy's son, Scorpius would their children then be pureblood by common belief? Or would Harry's being half-blood also mean his grand kids would be the same? What if their children in turn married another pureblood? Technically since Harry's mother was a muggle-born witch and his father was pureblood and Ginny was also pureblood, their children would have 3/4 blood purity. So one would think the line would resume "full" purity if Harry's child married a pureblood. *Note: I'm not talking about the perspective of Voldemort and his followers, who would argue Ginny's status as a blood traitor and would claim that any traceable muggle-born lineage would taint the blood.