I might be useful to implement a generic version of set_zero!.
Right now, it is used in different places to reset arrays (also others than du), thread-parallelized for the last entry.

E.g. in

    # TODO: Do not abuse `reset_du!` but maybe implement a generic `set_zero!`
    @trixi_timeit timer() "reset alpha" reset_du!(alpha, dg, semi.cache)

Originally posted by @sloede in #1736 (comment)