How to store CloudKit zone change tokens?

Question

So I currently use the following methods to get and set zone change tokens:

private func zoneChangeToken(for zoneID: CKRecordZoneID) -> CKServerChangeToken? {
    let cacheKey = self.name(for: self.database) + "." + zoneID.zoneName + "." + zoneID.ownerName
    if let data = UserDefaults.standard.data(forKey: cacheKey) {
        return NSKeyedUnarchiver.unarchiveObject(with: data) as? CKServerChangeToken
    } else {
        return nil
    }
}

private func setZoneChangeToken(changeToken: CKServerChangeToken?, for zoneID: CKRecordZoneID) {
    let cacheKey = self.name(for: self.database) + "." + zoneID.zoneName + "." + zoneID.ownerName

    if changeToken == nil {
        UserDefaults.standard.removeObject(forKey: cacheKey)
    } else {
        let data = NSKeyedArchiver.archivedData(withRootObject: changeToken!)
        UserDefaults.standard.set(data, forKey: cacheKey)
    }
}

I try to uniquely target the zone by creating a path from database to zone. However since the shared database might have multiple zones with the same zone name, I appended the zone owner name.

The question is, is this a proper way to store the zone change tokens or is there a better, more efficient, way?