Not able to clear Javascript Memoized function cache

I am trying to clear the memoized cache object but tried different solutions like prototype, call and bind but not able to make it work. Any help would be appreciated.

function memoize(func) {
  let cache = {};
  return function() {
    function clear() { cache = {}; }
    const key = JSON.stringify(arguments);
    if(cache[key]) { return cache[key]; }
    const result = func.apply(this, arguments);
    cache[key] = result;
    return result;
  }
}

function square(num) {
  console.log('calling square of', num);
  return num*num;
}

const memoizedSquare = memoize(square);

memoizedSquare(1);
memoizedSquare(1);
memoizedSquare(2);
memoizedSquare.clear(); // getting error on this line
memoizedSquare(2);
memoizedSquare(3);

function addition(a,b,c,d) {
  console.log('calling addition of', a,b,c,d);
  return a+b+c+d;
}

const memoizedAddition = memoize(addition);

memoizedAddition(1,2,3,4);
memoizedAddition(1,2,3,4);
memoizedAddition(4,2,3,1);
memoizedAddition(6,7,8,9);
memoizedAddition(6,7,8,9);