INT 2F U - DOS 3+ internal - FLUSH BUFFER
AX = 1215h
DS:DI -> disk buffer
SS = DOS DS (must be using a DOS internal stack)
STACK: WORD drives for which to skip buffer
ignore buffer if drive same as high byte, or bytes differ and
the buffer is for a drive OTHER than that given in low byte
Return: STACK unchanged
Note:   can be called only from within DOS

See also: 2F1209

2F1215 - DOS 3+ internal - FLUSH BUFFER