Reset other branch to current without a checkout

The workflows you describe are not equivalent: when you perform reset --hard you lose all the changes in the working tree (you might want to make it reset --soft).

What you need is

git update-ref refs/heads/OtherBranch refs/heads/CurrentBranch

Set otherbranch to point at the same commit as currentbranch by running

git branch -f otherbranch currentbranch

The -f (force) option tells git branch yes, I really mean to overwrite any existing otherbranch reference with the new one.

From the documentation:

-f
--force

Reset to if exists already. Without -f git branch refuses to change an existing branch.