Site blocked by robots.txt and 301 redirected still in SERPs

[VMLYRDiscoverability]

I have a vanity URL domain that 301 redirects to my main site.  That domain does have a robots.txt to disallow the entire site as well.

However, for a branded enough search that vanity domain still shows up in SERPs and has the new Google message of:

A description for this result is not available because of this site's robots.txt

I get why the message is there - that's not my , my question is shouldn't a 301 redirect trump this domain showing in SERPs, ever?

Client isn't happy about it showing at all.

How can I get the vanity domain out of the SERPs?

THANKS in advance!

[OlegKorneitchouk]

Add both sites to GWT, then go to: Vanity Site > Configuration > Change of Address > Select the new domain

Give it some time and G should replace the vanity url to the new domain.