Mexican Shredded Chicken

I am always disappointed about the options of Mexican food in the DC area. I am quite spoiled from living in the southwest for so long. So, I think I've come close to a classic shredded chicken recipe. I've used this for tacos, enchiladas, and burritos.

2 chicken breasts
1 medium onion, chopped
2 garlic cloves, minced
3 cups water
2 tablespoons butter
1 large tomato, chopped
1 teaspoon black pepper
1 teaspoon marjoram
1 teaspoon cumin
Salt to taste

In a medium sauce pan, boil the water. Add the chicken breasts, onion, and garlic. Boil for about 15 minutes, or until chicken is cooked through. Remove the chicken breasts and shred. Reserve one cup of the broth and dump the rest (or save broth for other dishes). In the same sauce pan, melt the butter over medium heat. Add the tomato, black pepper, marjoram, and cumin. Add the reserved one cup of broth. Continue to cook for about 15 minutes. Salt to taste and serve while hot.