My list looks like this:

* TODAY
** TODO Item 1
** TODO Item 2
* TOMORROW
** TODO Item 3
** TODO Item 4 

...as a single list, based on some advice I received here. I'd like to move TODO Item 2 from under TODAY to under TOMORROW.

The manual says:

M-up
M-down
Move the item including subitems up/down (swap with previous/next item of same indentation). If the list is ordered, renumbering is automatic. 

But while I can change the places of Item 1 and Item 2, I cannot move Item 2 outside of the Today heading---I cannot move it down under TOMORROW to proceed Item 3. The buffer tells me:

cannot move past superior level or buffer limit org mode

What is the keystroke that lets me move sub-items "past superior level" to under new headings?