In VBA, is there a way to tell when a key has changed?

For example, I have a list that users select from (in cell G10 - this is the
key), and under the list the users can enter some data associated with their
selection.

In the event they decide to go back and change their list selection (the
key), I would like to automatically clear out any input they already filled
so they can start again.

Any ideas?