How it works in Konsole:
All lines are shifted up until they disappear from the screen. They are available in the history.

XTerm and Linux console:
Everything visible on the screen is erased. Scrollback remains unchanged.

VT102 User Guide says:
"Erases complete display. All lines are erased and changed to single-width. Cursor does not move."
(those requirements are met in both cases. Scrollback was not available there, so nobody specified what to do with it.)

I think XTerm/Linux behavior is more appropriate here:
* It literally erases the characters, not shifts them up.
* Konsole by default sets 'TERM' to 'xterm-256color'
* 'clear' entry from terminfo gives strange effect (saves current screen in history, but removes everything else from it).