There might be better options, but you can look for the button and then click it with a script
Names Default To Here(1);
dt = Open("$SAMPLE_DATA/Cities.jmp");
nw = New Window("",df = dt << Data Filter(
Location({379, 384}),
Mode(Include(1)),
Add Filter(
columns(:Region, :POP),
Where(:Region == "MW"),
Display(:Region, N Items(6))
)
));
dt << Select Rows([1]);
btn = (nw << XPath("//ButtonBox[@title = 'Reset selection']"));
btn << click(1);
-Jarmo