C#: Check every value in a 2D array

I have a 2 dimensional array in my game:

   public int [,] grid = new int[3, 3] {
                 {0, 0, 0} ,   
                 {0, 0, 0} ,   
                 {0, 0, 0}   
            };

I am trying to have an if statement to check if every value not was zero. I know I could individually check every value but I was hoping for a more elegant solution.

public bool flag;
public int[,] grid = new int[3, 3] {
{ 0, 0, 0 },
{ 0, 0, 0 },
{ 0, 0, 0 }
};

void Start(){
	foreach(int i in grid){
		if(i != 0){
			flag = true;
		}
	}
}

If flag is true means you’ve got an element that is not 0