git branch | grep -v "master\|branchX"
(shows a list of to-be-deleted branches)
git branch | grep -v "master\|branchX" | xargs git branch -D
(deletes the branches from local)
git remote prune origin --dry-run
(shows the list of to-be-pruned branches)
git remote prune origin
(prunes the remote branches for local git object)