<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _mask_invalid(self, data, header):
 """Mask invalid data"""

        invalid = da.logical_or(data == header['block5']["count_value_outside_scan_pixels"][0],
                                data == header['block5']["count_value_error_pixels"][0])
        return da.where(invalid, np.float32(np.nan), data)