Hi Ross,
At the moment, this is scoped to the default target audience, which automatically includes all users in the domain and that audience cannot be modified or deleted.
But we can create a new audience and add it under Drive setting and make that as new defualt then remove the old audience from the list. However, if we remove the audience, I believe it will affect all existing files not shared with the domain.
Do you happen to know if there is an existing script that can be used to replace the current audience with a new target audience and then delete the previous target audience?