iCloud + CoreData - how to avoid pre-filled data duplication?

I have a problem with an iCloud shoebox application and hope some-one can help me (I've spent many hours fighting it in vain).

The App: - A simple library style application - containing set of categories (Cat1 .. CatN) each containing items (Item1...ItemM). I used Apple's iPhoneCoreDataRecipes to set up iCloud CoreData stack.

Everything works almost perfect with iCloud except - there should be a number of pre-filled empty categories the user can start using once he has opened the app for the first time (he can also be offline at that time). And here's the devil.

Here's what I do - Once my persistentStoreCoordinator is setup I send notification

dispatch_async(dispatch_get_main_queue(), ^{
    [[NSNotificationCenter defaultCenter]
        postNotificationName: @"RefetchAllDatabaseData"
                      object: self
                    userInfo: nil];
    });

which is received by my MasterViewController. When the notification is received MasterViewController checks the number of categories in the storage. If the number of available categories equals 0 - the pre-filled categories are inserted.

FYI - I use NSMergeByPropertyObjectTrumpMergePolicy for my ManagedObjectContext

The problem: This works well for the 1st device. But for the 2nd device the default categories from iCloud are often received later than persistentStoreCoordinator has been setup (and default categories inserted by 2nd device). In the end I have 2 sets of categories with the same names on both devices.

Any ideas how this can be solved?

Tried solutions: I tried 2 strategies to solve this. Both start in the same way. After I call

[moc mergeChangesFromContextDidSaveNotification: note];

I call

[self materializeKeysWithUserInfo: note.userInfo forContext: mo