I've tried to do a filter-branch like this to get rid of some large files:
git filter-branch --prune-empty --index-filter "git rm --cached -f --ignore-unmatch largedir*" --tag-name-filter cat -- --all
However, I see that the large objects are still in my repository in the 'objects' directory, even after a new clone. Is there a way to find out why these objects are still required according to git?