How to formally report database literature search results?
This sort of thing is pretty standard when it comes to meta-analyses, since each begins with a search for relevant studies. Generally, descriptions of the search query and its results are included in the methodology section of a paper; in addition to including the keywords used in the search (and, preferably, the reasoning for their inclusion), the start and end dates of the search should, as you mentioned, be noted. A diagram may also be helpful for readers to indicate the way in which you selected studies for analysis from the initial pool of results, and the languages in which the studies you assessed were written.

There are many papers that demonstrate this; as an example, "Psychosocial factors and chronic spontaneous urticaria: a systematic review" published in Allergy states the following:


  We first conducted a search of the PubMed and OVID/Medline databases
  using the keywords ‘urticaria’, ‘chronic urticaria’, ‘chronic
  spontaneous urticaria’ – given that the definition of CSU was not
  clearly established in early studies, we also included more general
  terminology such as urticaria and chronic urticaria, but excluded
  articles clearly assessing physical or acute urticaria –
  ‘psychopathology’, ‘stress’, ‘depression’, ‘anxiety’ ‘life events’ and
  ‘axis I’ and ‘axis II’, including full-text accessible articles in
  English, French and Spanish. We then performed a meta-analysis that
  included all these studies (see Fig. 1) from 1 January 1935 to 1
  January
  2012. After two reviewers (M.B.S. and I.B.) independently evaluated all potentially relevant studies, we conducted statistical analyses
  using Stata® version 12 (StataCorp LP, College Station, TX, USA).
  Methodological quality of included studies In order to assess the
  quality of the aforementioned studies, we employed a standardized
  measure specifically tailored to this systematic review, based on the
  Newcastle-Ottawa Scale (NOS) (8). This approach included the appraisal
  of external and internal validity, as well as biases common to
  observational studies specific to CSU and psychosocial factors. The
  independent reviewers mentioned above evaluated the study quality
  separately and resolved the differences in opinion by consulting a
  third reviewer (A.R.) (Table 1).


To sum up:


Databases searched
Search terms used (potentially alongside their justifications)
Dates of publication included in search
A diagram which explains how you winnowed these studies down to the relevant ones (and a table for the ones you decided to include in your paper)
As a bonus, if multiple authors are responsible for assessing studies for inclusion in your paper, include how these decisions were made/conflicts resolved.


I've bolded some of these ideas in the paragraph above to give yo a good idea of how this works.