If you have enabled Discovery for your Lync Federation services, you may want from time to time to add discovered domains to Federated Domains list to allow you to control their allow/block status.
Rather handily, Microsoft made this really simple to do.
Open the Event Viewer on one of your Edge servers and filter for Event ID 14601. You should find one of these logged every hour. This will contain the following:
Report of discovered partners that the Access Edge Server is currently monitoring.
There are 1 discovered partners, identified by the common name of their certificate.Name: accessurl.domain.com; Domains: domain.com
You can use these details to populate the Domain and AccessEdge fields in the Federation Domains section of your Lync Control Panel.