How observe Userdefault changes for com.apple.configuration.managed

I have an app which uses MDM settings pushed from Miradore.

I can read out the settings using:

NSDictionary *serverConfig = [[NSUserDefaults standardUserDefaults] dictionaryForKey:"com.apple.configuration.managed"];

I want to add an observer to only trigger a function when "com.apple.configuration.managed" is changed and no other NSUserDefaults value.

Currently the observer is triggered for all NSUserDefaults changes. The code for this that I have is:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(readDefaultsValues:) name:NSUserDefaultsDidChangeNotification object:nil];

Does anyone know how to only observe changes to "com.apple.configuration.managed"?