1. A method to operate at least one computer for searching a search space comprised of domains each representing a collection of related documents, comprising: establishing a domain characterization model (DCM) comprising a DCM index containing sets of individual keywords and keyword combinations, each set characterizing a context of a particular domain of a plurality of domains of a search space, where the DCM index includes at least one entry comprised of individual keywords and keyword combinations of the set and an identification of the particular domain where the individual keywords and keyword combinations of the set are found; and automatically in response to an original search query: operating a domain context matcher against the DCM index to identify at least one relevant search subject context for the original search query and to identify keywords and keyword combinations for each identified context; identifying, using the DCM index, at least one particular domain of the plurality of domains from the identified relevant search subject context and the identified keywords and keyword combinations; processing the identified set of keywords and keyword combinations for each of the identified at least one particular domain to select at least one of the keywords or keyword combinations most relevant to enhance the original query and associated with the identified at least one particular domain; forming at least one enhanced domain-specific search query, said at least one enhanced search query being formed for targeting the identified at least one particular domain and comprising the original search query and the selected at least one keyword or keyword combination; and searching the identified at least one particular domain of the plurality of domains using the enhanced search query.