Synchronize the scroll offset of a vertical split

Question

Set up

• Left (L) and right (R) are two vertically split windows displaying the same file.
• No other windows exist in the tab.
• The uppermost displayed line in L is x (Lx) and the uppermost line in R is y (Ry).
• The focused window is denoted by an asterisk (*L or *R).

Question

I am looking for a normal mode map to do this:

1. If L has focus: Change *Lx Ry into *Lx Rx.
2. If R has focus: Change Lx *Ry into Ly *Ry.

I.e., I want the offset between the windows to be zero.

Attempts

syncbind almost solves the problem, but since it requires both windows to have scrollbind set, and I rarely have it set, things get more complicated. windo would apparently solve it:

noremap <F11> :windo set scb<bar>syncbind<CR>:windo set noscb<CR>

But although it works properly for case 2, it fails for case 1 because it shifts focus to the right window.

Answer 1

noremap <expr> <F11> winnr()==1 ?
    \ ':windo set scb<CR><C-W><C-W>:syncbind<CR>:windo set noscb<CR><C-W><C-W>' :
    \ ':windo set scb<bar>syncbind<CR>:windo set noscb<CR>'

I have a strong feeling this solution exceedingly verbose and can probably be optimized, but it does the job.