Same site but changed address. Google not indexing new site?

Hi guys, I need some help here.

I've been using my domainA.com for number of years.
Recently, I have decided to re-brand my business and purchased domainB.com

Both domains are hosted on the same server (same cpanel - not sure if that matters).
And 1.5 months ago, I applied 301 redirect on DomainA.com htaccess

Redirect 301 / http://domainB.com

Click to expand...

That script works, all traffic from DomainA.com now redirects to DomainB.com successfully.

However, Google still has DomainA.com INDEXED, and DomainB.com is partially indexed (not the entire site for some reason).
I thought by using "301 Redirect", Google should automatically recognize that the site has moved permanently?

Since both site has the same content, I am concern that I might even be hit with duplicated content issue in this case.

So what should I do moving forward? Why isn't DomainA.com deindexed yet? I want it's existing ranking to transfer to DomainB.com

Did you use the 301 redirect correctly?

there must be some issue in redirection.