How do I 'overwrite', rather than 'merge', a branch on another branch in Git?

Question

I have two branches, email and staging. staging is the latest one and I no longer need the old changes in email branch, y

Answer 1

Other answers looked incomplete.
I have tried below in full, and it worked fine.

NOTE:
1. Make a copy of your repository before you try below, to be on safe side.

Details:
1. All development happens in dev branch
2. qa branch is just the same copy of dev
3. Time to time, dev code needs to be moved/overwrite to qa branch

so we need to overwrite qa branch, from dev branch

Part 1:
With below commands, old qa has been updated to newer dev:

git checkout dev
git merge -s ours qa
git checkout qa
git merge dev
git push

Automatic comment for last push gives below:

// Output:
//  *<MYNAME> Merge branch 'qa' into dev,*  

This comment looks reverse, because above sequence also looks reverse

Part 2:

Below are unexpected, new local commits in dev, the unnecessary ones
so, we need to throw away, and make dev untouched.

git checkout dev

// Output:
//  Switched to branch 'dev'  
//  Your branch is ahead of 'origin/dev' by 15 commits.  
//  (use "git push" to publish your local commits)


git reset --hard origin/dev  

//  Now we threw away the unexpected commits

Part 3:
Verify everything is as expected:

git status  

// Output:
//  *On branch dev  
//  Your branch is up-to-date with 'origin/dev'.  
//  nothing to commit, working tree clean*  

That's all.
1. old qa is now overwritten by new dev branch code
2. local is clean (remote origin/dev is untouched)