Dominguez had a message to the hooligans, known as barrabravas in Argentina, should they be thinking off attending the match.
But a day later, Boca refused to play again, insisting they would be disadvantaged, and the match was indefinitely postponed.
River and Boca are the two most popular teams in Argentina, allegedly commanding between them 70 percent of the country's football fans. Miami; Asuncion, Paraguay; Medellin, Colombia; and Doha, Qatar, were reportedly in contention along with Madrid, which will now host both the Copa Libertadores and Champions League finals in the same season, with the latter being played at Atletico Madrid's Wanda Metropolitano on June 1.
Dominguez added the game would be staged at Real Madrid's Bernabeu stadium at 8:30 pm.
It remains to be seen how the clubs take the news.
South American soccer's governing body rejected a request by Boca to be declared winners, but has fined River $400,000 and ordered the club to play the next two CONMEBOL games behind closed doors.
A statement released on Thursday evening by CONMEBOL president Alejandro Dominquez read: "The administration has elected to hold the Copa Libertadores final return leg, in front of both sets of supporters, in Madrid at the Santiago Bernabeu". The Copa Libertadores victor is South America's entrant in the FIFA Club World Cup, which kicks off December 12 in the United Arab Emirates.
Boca Juniors are not happy with the decision and will appeal to CONMEBOL's Chamber of Appeals and, eventually, the Arbitration Court of Sport.
The tournament kicks off on December 12 with the South American representative playing their first match on December 18. The G20 summit, which began in Buenos Aires on Friday, is going to have to go some ways to match the knot of complaints that have dominated the local media since November 24, when the original tie was supposed to take place.