Destroy GameObject won't destroy

Hi, I have a prefab instance which I am instantiating and destroying thus:

public var block : GameObject = null;

block = Instantiate(blockPrefab, originVector, Quaternion.identity);

Destroy(block);

The block is disappearing on Destroy. However the null comparison is not executing and I can still query transform info, attach textures etc!:

if (block == null) {//not happening}, block.transform.position, block.renderer.material.mainTexture = Resources.Load("pink"); (the last 2 excerpts do not throw a NullPointerException)

If I remove the Destroy call, the object is there and rendered pink. I read Destroy nullifies a GameObject, or at least this (block == null) would return true. But it's not. Any ideas pls?

Thanks