How should garbage collection be implemented?

[mrpmorris]

When normalizing data I end up with state that looks like this

users: {
UserId1: ...instance of user...
UserId2: ...instance of user...
}

The problem with this is obviously that it will continue to grow over time. Does anyone have a working solution that identifies when a certain slice of state is no longer in use (e.g. "users") so I can dispatch an action to clear it down?

[robwormald]

Please take "how-to" questions to gitter - https://gitter.im/ngrx/platform - GitHub is for bugs and issues. Thanks!