The xrefresh command will do that.
$ man xrefresh
xrefresh - refresh all or part of an X screen
xrefresh [-option ...]
Xrefresh is a simple X program that causes all or part of your screen
to be repainted. This is useful when system messages have messed up
your screen. Xrefresh maps a window on top of the desired area of the
screen and then immediately unmaps it, causing refresh events to be
sent to all applications. By default, a window with no background is
used, causing all applications to repaint ‘‘smoothly.’’ However, the
various options can be used to indicate that a solid background (of any
color) or the root window background should be used instead.