If I remember correct Damus stuffs the relays list in the contact list, but there is no spec for that, in the past this would clear your (Damus) relays if you follow/unfollow someone in Nostur but I changed it to keep whatever is there so that doesn't happen anymore.

So if you are testing other clients, a follow/unfollow would probably do it. Nostur doesn't publish any relays at the moment, except for the ones you already have published as I'm still working to implement NIP-65 (Relay List Metadata)