Contact Framework equivalent to ABAddressBook.ABAddressBookRegisterExternalChangeCallback

I am migrating an application from the deprecated Address Book Framework to the new Contacts Framework. The application utilizes ABAddressBookRegisterExternalChangeCallback to be notified when another application changes a contact.

I am unable to find equivalent functionality in the Contacts Framework. Apple documentation says to use the default notification center with the CNContactStoreDidChangeNotification notification:

The notification posted when changes occur in another CNContactStore.

Taking Apple's advice, my code looks like this:

NSNotificationCenter.defaultCenter().addObserver(
    self,
    selector: "contactsChanged:",
    name: CNContactStoreDidChangeNotification,
    object: nil)

However, I have found two problems with this approach:

1. I am notified for all changes, including those made by my own application.
2. Notifications are spurious - I receive many notifications for a single change.

If I log the debug description of the notification when the change was made within my app, I get something like this:

NSConcreteNotification 0x7d3370e0 {name = CNContactStoreDidChangeNotification; userInfo = {
    CNNotificationOriginationExternally = 1;
    CNNotificationSourcesKey =     (
    );
}}

And if the changes are made externally:

NSConcreteNotification 0x7bf7a690 {name = CNContactStoreDidChangeNotification; userInfo = {
    CNNotificationOriginationExternally = 1;
    CNNotificationSourcesKey =     (
    );
}}

As you can see, nothing obvious with which to distinguish them.

Can anyone tell me how to get the same behavior from the Contacts Framework as one can get from ABAddressBookRegisterExternalChangeCallback?