[git] git still shows files as modified after adding to .gitignore

The solutions offered here and in other places didn't work for me, so I'll add to the discussion for future readers. I admittedly don't fully understand the procedure yet, but have finally solved my (similar) problem and want to share.

I had accidentally cached some doc-directories with several hundred files when working with git in IntelliJ IDEA on Windows 10, and after adding them to .gitignore (and PROBABLY moving them around a bit) I couldn't get them removed from the Default Changelist.

I first commited the actual changes I had made, then went about solving this - took me far too long. I tried git rm -r --cached . but would always get path-spec ERRORS, with different variations of the path-spec as well as with the -f and -r flags.

git status would still show the filenames, so I tried using some of those verbatim with git rm -cached, but no luck. Stashing and unstashing the changes seemed to work, but they got queued again after a time (I'm a bity hazy on the exact timeframe). I have finally removed these entries for good using

git reset

I assume this is only a GOOD IDEA when you have no changes staged/cached that you actually want to commit.