I know this is an old thread but I just stumbled across.
So heres how I would do it, with your local template variable on the input field you can set the value of the input like below
<input mdInput placeholder="Name" #filterName name="filterName" >
@ViewChild() input: ElementRef
public clear() {
this.input.NativeElement.value = '';
}
Pretty sure this will not set the form back to pristine but you can then reset this in the same function using the markAsPristine()
function