There is only one form of true door slam. It either is, or is not. If you are willing to interact with, or include, that person in your life again, it is not a door slam. I don't do this often, but when I've done it I really mean it.
If I don't think I can live my entire life without interacting (due to ties I cannot break), even if I don't want to interact, I just avoid them, but that is not door slamming. I also do not door slam anyone I still have feelings about, even if those feelings are pure anger, because emotion fills space.
I'm not really sure where it comes from.
Ni and Fe?
Fe users are susceptible to others' emotions, so we cut off any situation where we could be vulnerable to the toxic person's emotions.
(Lacking Fi) we also lack finesse with deciphering our own emotions, which may (or may not) contribute to the INFJ's famous habit of either caring very deeply or not at all. (And also contributes to not really knowing where door slamming comes from!) Once a person is in the 'not at all zone', we aren't tempted to keep "picking at the scab" so to speak. We don't have feelings for you, and to keep from "ingesting" your feelings we door slam to keep you away from us. I end the risk of absorbing that person's feelings by cutting them out of my reality in every way.
It seems like all the people I deeply care about (romantic love, family, friends, those I respect, favorite musicians, artists, authors, etc) exist in Ni as much as in Fe and (Shadow)Fi. Average people do not inhabit my Ni, even if I “like” them. I feel compassion for all, but they don't get a special gear in my brain. All kinds of people get gummed up in my Fe. Fe is open territory, including for people I would not necessarily invite to be there, so the safest way to keep the "dead to me" people truly away, is to banish them forever.