D:\...>sfdx force:org:list
=== Orgs
ALIAS USERNAME ORG ID CONNECTED STATUS
─── ──────────── ────────────────────────────────────────── ────────────────── ────────────────
DevHub [email protected] 00D7F0000000001AAA invalid_grant
I just had my trial Dev Hub org expire (invalid_grant), so I created a new Dev Hub and registered it with sfdx force:auth:web:login -d.
That moved the (D) marker to my new dev hub, but the old one was still hanging around. Peter's solution would have worked, but I thought I'd try a sfdx force:org:delete -u DevHub to see what happens now the old org is no longer the nominated dev hub.
D:\...>sfdx force:org:delete -u DevHub
Enqueue scratch org with name: DevHub for deletion? Are you sure (y/n)?: y
Successfully deleted scratch org DevHub.
Appears to have worked even though it isn't a scratch org. The old dev hub org no longerslonger appears for a sfdx force:org:list