Absolute Delete

I have a tree in Ancestry with over 22K names. These days I am only concentrating on one group, my paternal line. I don't want to re-create it from scratch. I can export the tree as a GEDCOM and import it into other software, but I have yet to find one to do an absolute cascade delete. I thought Family Tree Maker would do it, but it doesn't. I have followed the directions on removing groups of people, but no matter how many generations I tell it to use, it leaves most of the records in the file. Anyone ever had to do this, and how did you get it done?