Added in 1.7

/aclear [-agmnqstu]

Clears the buffer and Switchbar/Treebar 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