Added in 1.7

/aclear [-agmnqstu]

Clears the buffer and Channelbar/Sidebar unread color of the specified window type, if no type is specified, all windows on current connection is cleared.

Switches

-a - all windows on all connections
-g - TODO
-m - TODO
-n - channel windows
-q - query windows
-s - status windows
-t - dcc chat windows
-u - custom windows

Example

; Clear all channel and query windows.
/aclear -nq

; Clear all windows on current connection.
/aclear