ok lets see, there are a few ways of pulling it off. I am not sure how dominion handles it, but two really good examples are Master of magic and Heroes of might and magic.
They do it in different ways,in master of magic you have "units".
each unit can have between 1 and 8 individuals in it.
when it attacks, each individual in the unit makes an attack roll and each roll is dealt with seperately.
meaning that 8 spearmen can each make a str 2 attack -> 8 to hit rolls are made and managed. Each spearman has 3 hp so that the whole unit needs to take 24 point of damage to be wiped out. If the unit levels and gain hp, they go up to 4 hp each, so the unit goes up to 32 hp in total. All attacks go against the same spearman until it is killed, then move on to the next one. Area attacks hit all of the at the same time, such as a fireball, so a str 5 firebal has the potential to outright kill the whole stack, whereas the firebolt spell would attack them one at a time until it ran out of damage (it would have to be at least a 24 damage firebolt for a perfect roll kill which would not happen, it's max damage was 20 for this spell)
The minotaur was a 2 individual unit, high str, high defence, high hp - it's effectiveness cut in half if you killed one of the indivuals.
lesse in Heroes of might and magic
you have a stack of 10 peasants. 3 hp each, attack of 2, defence 2.
the skills of the hero completely change how they react in combat. Hmm on second thought, they are more similar than i initialy believed.
Hmm we will need more examples from other people, i have been writing for several hours now and i am drawing a blank.
EDIT HA kenata beat me taht was odd seeing his post there