Google benchmark: flush the cache for every function call without timing it

Question

I'm using Google benchmark to time a function, but I need to see how it performs when working with a "cold" cache. I know the benchmark library will run a function until the timing is steady, but I would like this steady timing to incorporate the fact that the cache is cold. This is roughly what my benchmarking looks like:

template <class ...Args>
void BM_MyFunc(benchmark::State& state, Args&&... args) {
    auto args_tuple = std::make_tuple(std::move(args)...);
    const int arg = std::get<0>(args_tuple);
    for (auto _ : state) {
        // flush cache by accessing a huge array
        for (int i = 0; i < N; i++) {
            huge_array[i] = rand();
        }
        my_func(arg);
    }
}

BENCHMARK_CAPTURE(BM_MyFunc,  my_func_with_42,  42);

The problem is that putting the cache flushing inside for (auto _ : state) means that the actual act of flushing the cache appears to be part of the timing results. If I put the cache flushing outside that loop, then the cache is only flushed once and the benchmark library treats it as a bad thing and warms up the my_func so that it's not working with a cold cache.

Is there some way to have a "per function-call" setup that doesn't contribute to the timing of said function? The documentation doesn't seem to cover this particular use case.