how to only destroy certain blocks?

hey just wondering how i could make this code only destroy blocks that have been made not original? or to not destroy certain objects say blocker or somthing?

var blockPrefab : GameObject;
var hit : RaycastHit;
var range : float = 4;
var blockLayer : LayerMask = 1;
function Update () {
    if (Input.GetMouseButtonDown(0))
    if (Input.GetMouseButtonDown(1))
function PlaceBlock() {
    if (HitBlock()) {
        var cube = Instantiate(blockPrefab ,hit.transform.position + hit.normal, Quaternion.identity); 
function DestroyBlock(){
function HitBlock() : boolean{
    return Physics.Raycast(transform.position, transform.forward, hit, range, blockLayer);

One option is to set the tag variable of the instantiated cube to something like “Blocker” then in your check for hitting a block you can check if the GameObject’s tag matches. Eg.

function HitBlock() : boolean{
    if(Physics.Raycast(transform.position, transform.forward, hit, range, blockLayer))
        if (hit.collider.gameObject.tag == "Blocker")
            return true;

    return false;