Grandad 'nagging' is not limited to domestic chores, even though it occurs mainly in relationships.
As Grannygravy points out, when she was accuse of 'nagging' she was reminding someone of an engagement and I am sure I am not the only one accused of 'nagging' over medical concerns.
Essentially the word is used by someone who is being reminded of something they haven't done that they feel defensive about, because they know they should have done it - and that covers a very wide field.
Another silly little ABC game - shops we have loved and lost?