How can I fix the problem I'm having moving an object between two specific locations?

I have the code to move an object between two specified locations in javascript, the object moves from the first point to the second without a hitch however when it reaches the second point and tries to return to the first point it wont because it fulfills both requirements in the code so it stays in the same position after reaching the second point.
This is what I have so far if anyone can help id be grateful.

pragma strict

var directionMovement: String = "Movement2";

function Start () {
	//directionMovement = "Movement1";
}

function Update () {
	gameObject.transform.rotation.y = 0;
	gameObject.transform.rotation.x = 0;
	Move(); 
	if (directionMovement == "Movement1") { 
		gameObject.transform.Translate (0,0,-0.1); 
	} 
	if (directionMovement == "Movement2") { 
		gameObject.transform.Translate (0,0,0.1); 
	}
}

function Move() { 
	Debug.Log("gameObject.transform.position.z = "+gameObject.transform.position.z); 
	if (gameObject.transform.position.z <=90) { 
		Debug.Log("going right"); directionMovement = "Movement2"; 
	} 
	if (gameObject.transform.position.z >=60)
	{
		Debug.Log("going left"); directionMovement = "Movement1"; 
	} 
}

Now that the code is readable I can see what you mean.

Just change your if statements like so:

 if (gameObject.transform.position.z >=90) { 
       Debug.Log("going right"); directionMovement = "Movement2"; 
    } 
    if (gameObject.transform.position.z <=60)
    {
       Debug.Log("going left"); directionMovement = "Movement1"; 
    } 

This way it will change direction when reaching the point or if it goes a bit over them.

What you did before could never work becuse both if statements where true.