Spawn after completion of drag and drop

I am a beginner at Unity and C# and I have started off by making pieces of games instead of whole games to understand how to make a whole game. I have accomplished making a simple drag and drop by mixing some tutorials and samples together with the following below:

using UnityEngine; using System.Collections; public class InputManager : MonoBehaviour

{ private bool draggingItem = false; private GameObject draggedObject; private Vector2 touchOffset;

 void Update()
 {
     if (HasInput)
     {
         DragOrPickUp();
     }
     else
     {
         if (draggingItem)
             DropItem();
     }
 }

 Vector2 CurrentTouchPosition
 {
     get
     {
         Vector2 inputPos;
         inputPos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
         return inputPos;
     }
 }

 private void DragOrPickUp()
 {
     var inputPosition = CurrentTouchPosition;


     if (draggingItem)
     {
         draggedObject.transform.position = inputPosition + touchOffset;
     }
     else
     {
         RaycastHit2D[] touches = Physics2D.RaycastAll(inputPosition, inputPosition, 0.5f);
         if (touches.Length > 0)
         {
             var hit = touches[0];
             if (hit.transform != null)
             {
                 draggingItem = true;
                 draggedObject = hit.transform.gameObject;
                 touchOffset = (Vector2)hit.transform.position - inputPosition;
                 draggedObject.transform.localScale = new Vector3(1.2f, 1.2f, 1.2f);
             }
         }
     }
 }

 private bool HasInput
 {
     get
     {
         // returns true if either the mouse button is down or at least one touch is felt on the screen
         return Input.GetMouseButton(0);
     }
 }

 void DropItem()
 {
     draggingItem = false;
     draggedObject.transform.localScale = new Vector3(1f, 1f, 1f);
 }

}

I was wondering how I would go about having there be only specific places where the drop of the drag and drop could be completed? So, if I had a 9x9 grid made of prefab squares with 2D colliders on them meant to act as a board, how would I ensure that the game piece that I am dragging can only ever fall onto one of these 9 game board tiles?