It's not only the name -- it's the exact query you're running.
<cfquery name="getPeople" cachedwithin=".5" ...>
select name from employee order by name
</cfquery>
If you invoke this same query anywhere else in your app, you'll get the cached version if it's within half a day of the first query. But these will hit the database for fresh data:
<!--- Different name, same SQL: A new cached query --->
<cfquery name="getEmployees" cachedwithin=".5" ...>
select name from employee order by name
</cfquery>
<!--- Different SQL, same name: Redefining the cached query --->
<!--- Note: As pointed out in comments, it's not really overwriting the old query
of the same name, but making a new one in the cache. The first one by the
same name is still in the cache, waiting for eviction (or use). --->
<cfquery name="getPeople" cachedwithin=".5" ...>
select name from employee order by name desc
</cfquery>
And yes, it does take a variable into account. If you use cfqueryparam -- which you should be doing -- your database will cache the query plan, but even using cachedwithin, each query with a changed parameter will be treated as different from a query caching perspective. Note that this means if you use cachedwithin on a query that runs many times with different parameters, you'll be flooding your query cache with queries that have low cache hit rates.