The ornamental design for a grillbrush, as shown and described.
FIG. 1 is a right side elevational view of a grill brush showing our new design, the left side being a mirror image;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a front elevational view thereof; and,
FIG. 5 is a rear elevational view thereof.
The bristles are partially shown for ease of illustration, it being understood that each set of bristle groups extends radially from the twisted support as shown by the front group in FIG. 1 and the two side groups in FIG. 5.