Parents try to impart their values, but indoctrination for me begins where they won't allow their children to come to their own, potentially disagreeing opinions. Prohibiting contact to peers with other views, that sort of thing.

You can impart values on children and try to lead by example, but ultimately, they're sovereign individuals, not their parents' property. It's the unwillingness to accept that where I see education and guidance cross the border into indoctrination.

A far better qualifier than my "I know it when I see it", for someone pretty certain they weren't indoctrinated, would probably be a grown-up's reflection on their own upbringing. If they're lucky and become an independent person, they will have a good feeling about whether their upbringing involved unacceptable levels of coercion and isolation.