How to reset the hashset back to original data after intesection

[Kath_Fish]

hi...i am doing the intersection now.I need to reset my hashset,hs2 to original data after it intersect with the first data set. So that, it can continue to intersect with the second data set.
here is my coding:

for (int i = 0; i < myArray1.Count; i++)
           {
               foreach (string t in myArray1[i].ToString().Split(' '))
               {
                   ItemKey.AppendText(t);
                   hs3.Add(t);
               } 
               hs2.IntersectWith(hs3);
               foreach (string y in hs2)
               {
                   MessageBox.Show(y);
               }
               hs2.Clear();
               
               hs3.Clear();
           }

hope someone can help me..thank you so much.