Run this example in Remix + debug it to show that memory is erased between function calls

MemoryBetweenCalls.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Source {
    Target target;

    constructor(Target _target) {
        target = _target;
    }

    function callTarget() public {
        target.doSomething();
    }
}

contract Target {
    function doSomething() public {
        // do whatever
    }
}