Force Operation on Remote Database

Question

I have a 3 part UNION ALL query, each part of which runs against a different DB via DB links (the 1st part runs against the local DB).
When I run each part that accesses the remote DB, the query runs totally remotely and runs in under 5 seconds.
However, when I combine them into one query, I see REMOTE inside of a nested loop structure, and the query takes around 20 minutes. No part of the query depends on anything on the local machine; I've had that reviewed. (I also have about 20 other queries with the same structure that generate correct explain plans).
I have verified that the subquery can and should run totally against the remote DB.
Is there any way to force the query to be executed remotely?
The portion of the explain plan looks like this:
SORT GROUP BY
..nested loops
....nested loops
......remote
......remote
....remote
..remote

Answer 1

Tried driving_site with the following results:
1. Local query and 1 remote query with driving_site - works fine!
2. Local query and 2 remote queries each with driving_site - driving site is ignored, back to nested loops
3. Local query 1 remote query with driving site and 1 remote query without driving site - get
ORA-22992: cannot use LOB locators selected from remote tables
ORA-02063: preceding line from PROD
ORA-02063: preceding 2 lines from PDSPROD_B
Note that there is a CLOB in one of the tables, but I am not using that column in the query.
The subqueries look like this:
SELECT /*+ driving_site (c2 ) */ c2.company_name, COUNT (b.customer_id), c2.company_id,
c2.super_domain_info_id, sd2.brand_full_name, &&cl_id_3 AS CLUSTER_ID
FROM v_user_info&&cluster_link_3 b,
company_info&&cluster_link_3 c2,
user_audit_info&&cluster_link_3 u,
super_domain_info&&cluster_link_3 sd2
WHERE b.company_id = c2.company_id
AND b.customer_id = u.customer_id
AND c2.super_domain_info_id = sd2.super_domain_info_id
AND b.account_type = 0
AND b.active_in_company = 'Y'
AND b.company_id NOT IN
(5982737, 5982906, 5982712, 5982736, 5982908, 5977782, 11,
2085412, 2134043, 5874338, 2, 5979364, 5979363, 6, 5980943,
5981023, 12, 5978042, 5922312, 5979201, 5977961, 5982603,
5978602, 5978001, 5981903, 5981423, 5978523, 5879286, 5978284,
5977941, 5977661, 5977801, 5982185, 200, 5978524, 5982603,
5979562, 5979963)
AND u.first_login_time <> TO_DATE ('01/01/1900', 'MM/DD/YYYY')
AND c2.current_membership_id IN (
SELECT cm.ID
FROM cluster_membership&&cluster_link_3 cm
WHERE cm.CLUSTER_ID = &&cl_id_3)
GROUP BY c2.company_name,
c2.company_id,
c2.super_domain_info_id,
sd2.brand_full_name