How to forcefully delete a remote branch in GitHub?

Question

I have 2 remote branches :

 - pending-issues-in-project
 - new-issues-in-project

I tried to delete pending-issues-in-project like this :
git push origin :pending-issues-in-project, but i got the error :

error: unable to push to unqualified destination: pending-issues-in-project
The destination refspec neither matches an existing ref on the remote nor
begins with refs/, and we are unable to guess a prefix based on the source ref.  
error: failed to push some refs to '[email protected]:forkedRepo/RepoName.git'

So i thought may be i have deleted pending-issues-in-project branch, but when i run
git branch -a it shows pending-issues-in-project branch in the list.
When i tried same (tried deleting) for new-issues-in-project, it worked.
I have already deleted both branches from local server using git branch -D branchName.

If the error is coming because the branch not exist in repository then why its coming in remote branch list?
and
Is there any way to forcefully deletion of the remote branch?

Thanks for your time.

Answer 1

You have to do:

git remote prune origin

to remove that remote tracking branch in your local git repository ( prune removes any branch that does not exist in the remote origin anymore). After that, you will not see it under git branch -a